Producing clean fresh water is critically important worldwide. As the demand increases linearly with the world's population, and the supply of fresh water decreases, the challenges to produce adequate amounts of fresh water are increasing daily.
Known desalination systems, including those that rely primarily on solar energy, operate and produce fresh water, but very slowly and often inefficiently. Yet, observing the planet's weather, and rain patterns, one can't help wonder why this has to be. If nature can efficiently produce large amounts of fresh water (e.g., rain) from salt water, why can't we? This isn't a trivial question, but rather it's a question of great and tremendous import. We must explore what is wrong with the current attempts at desalination, and explore the differences between manmade solar desalination methods and devices and those used by nature. If we can learn to, in a sense, imitate the sun and earth, then we can on command, potentially produce large quantities of more fresh, clean, drinking water; without having to resort to outrageously expensive and inexpensive systems, such as those based on reverse osmosis.
In many places on the planet, fresh water is the single biggest critical human (and animal) health issue. Approximately 40% of the earth's population lives on an ocean shoreline, with approximately 85% of the population living within 60 miles. In addition, around three quarters of the world's mega cities are by the sea, where there is no lack of salt/saline water.
The basic concepts of manmade desalination have not been challenged, let alone significantly changed, in years. The underlying concepts and principles of today's desalination devices are simply wrong. For example, nearly all, if not all, manmade desalination devices made to date rely on a container (or pipe) of some size, with some amount of salt/brackish/dirty water comprising the “containment reservoir,” and in the non-pipe configuration, a sealed cover over to allow the evaporative vapor to condense and form water drops that are then gravity fed into a storage tank. Some have reflective mirrors of various sizes (large and/or small) directing sunlight into the device. None of the devices, however, work and generate an appreciable amount of fresh water in the absence of sunlight.
Known devices rely on a static, sedentary, flat/horizontal, environment. In contrast to nature, current desalination solar stills are horizontal/level, motionless, immobile, and inanimate. This results in a plethora of problems.
Many of the shortcomings of known methods are rooted in basic molecular water chemistry and physics. Water is composed of self-hydrophilic, strongly bipolar/dipolar, highly charged hydrogen/oxygen molecules. In other words, water molecules like to stick to themselves. Indeed, water molecules literally are bonded and don't want to leave each other. This is particularly the case at the water's surface. These forces bind water molecules to each other like a kind of magic/magnetic glue to form a surface or interfacial tension. Everyday examples that highlight this phenomenon include an insect walking on water, the famous straight pin lying on top of the water's surface in a glass, and the minimal surface shape of a water droplet. Water's dipolarity attraction (hydrogen bonding) also enables molecules to “stick” to each other and climb up surface, for example, inside tube surfaces. It should be noted, however, that in general surface tension (air/water interface) always develops on flat/horizontal/undisturbed surfaces.
Gravity is an additional force acting against current (horizontal) desalination methods and devices. Most all solar desalination systems, multi-effect and otherwise, simply do not exploit this principle and are designed to lie in a single, flat and/or, horizontal plane; a critical error.
Known methods and systems also include static, unmoving air hovering above the water. Such configurations rely on the “chance” that water vapor could/might eventually contact and “attach” itself to the still's capture surface area and condense to form droplets, but this is purely by “chance” and is in fact a small statistical probability.
In contrast to the static, unmoving manmade desalination systems of today, the Earth's environment, including heat, generates wind and waves, which constantly agitate both sea and air; stirring boundary layers of hot/cold water, mixing air into the ocean/sea below the water's surface, and mixing air into itself above the water's surface. Generally, Earth's system is in constant vibrating motion. Further, a huge amount of stored energy continues to generate fresh water even after the sun goes down.
The well-known Penman-Shuttleworth Evaporation Equation attempts to quantify this process and provide a minimum evaporation rate in gal/day:
      E          m      ⁢                          ⁢      a      ⁢                          ⁢      ss        =                    mR        n            +              γ        *        6.43        ⁢                  (                      1            +                          0.536              *                              U                2                                              )                ⁢        δ        ⁢                                  ⁢        e                    λ      (              (                  m          +          γ                )            
It is important to note, however, that while this equation is known, it does not, in any way, take into account or adjust for kinetics (other than wind speed) that are acting on the system—a fact that presents another fundamental flaw with the current understanding of evaporation and desalination.
What nature has evolved to “understand” is that surface tension tends to draw the surface molecules into the bulk of the liquid and by removing this force or “glue,” water molecules are more freely allowed to escape. In other words, if water is not allowed to form linear/flat surfaces against the air barrier, surface/interfacial tensions cannot form or are greatly decreased.
In nature, the sun's heat/light creates high/low atmospheric pressure zones, blowing water/air molecules apart from each other, while the wind and waves are stirring up the seas, rising and falling on itself, stirring together layers of aerated water, which rises to the atmosphere, and then utilizing gravitational pull, continually mixes, and stretches the water molecules, breaking surface tension. Such an effect can be easily seen in everyday life. Stir a cup of hot coffee or tea, for example, and observe the increase of steam (water vapor) that is released compared to a static, unmixed cup.
In science and chemistry, this addition of “energy”/(motion) into a closed system is mathematically described as/by the term “kinetics.” Kinetics is a critical component to driving chemical and biological reactions. Kinetics occurs on a macro (visible) scale and/or micro (invisible to the eye) scale. Thus, to efficiently and effectively promote evaporation and desalination, one must not only consider, but effectively employ, one or more kinetic energy inputs into the process.
In view of the foregoing discussion and state of manmade evaporative and desalination devices, aspects of the present disclosure are directed to producing fresh water from salt water in an efficient and economic manner, and overcoming problems/issues with known desalination devices. Generally, in current desalination devices a vessel is filled with salt/saline water and a cover is placed over the top of it. As water naturally evaporates, some percentage of the vapor attaches and condenses on the cover, forming droplets, which are pulled by gravity down the surface into a separate containment vessel.
Following is a non-exhaustive list of issues with known desalination systems that aspects of the present disclosure address to thereby provide optimal desalination: 1) water molecules “sticking” to each other at the water/air surface boundary (surface tension); not allowing/releasing molecules to “escape” or evaporate into the air; 2) stagnant air that isn't moving across the water's surface, therein not creating surface friction or breaking surface tension; 3) stagnant air that isn't being mixed into the water reservoir and isn't escaping up from the water and “towing” attached water molecules up with it; 4) humid condensing air that isn't being driven against/into the capture cover/membrane(s), rather it's left to probability and random chance; 5) flat/horizontal system that doesn't utilize gravity's force to stretch water molecules across the reservoir walls and surface, breaking surface tension molecular bonds; 6) the systems often don't create low pressure zone(s) where evaporative humid water vapor is generally (vacuum) released into the atmosphere, (note that the reverse—high pressure areas—force water vapor back into solution; 7) current systems haven't increased and maximized the key water/air surface area interface of the system; 8) many current systems have not increased the number of methods/mechanism(s) (effects/phases) that capture condensed and non-condensed water vapor, and rely entirely on collecting water vapor from only the surrounding cover membrane; 9) most current systems are closed systems, making them difficult to maintain, clean and/or remove deposited materials and are subject to clogging and restricted performance; 10) current systems that rely on solar energy generally only work during the day (even without sun during the night, fresh water still needs to be generated; water gathering storms don't stop at night, neither can our desalination systems); 11) current systems don't cool capture membrane/air to increase condensation; and 12) even most “advanced” current systems collect/use stored energy as heat and are dependent on AC power sources, i.e., the local power grid. Many known desalination systems, even solar, still require some AC power to run equipment like vacuum pumps, motors, etc. Economically, using AC power requires sacrificing large amounts of money or barrels of oil. Many/most areas on the planet don't have power grid access, thereby limiting the use of known systems.
To improve/increase evaporation, including solar production of fresh water, the present invention addresses the foregoing issues. Exemplary embodiments as disclosed provide an affordable, portable, (and scaled up fixed infrastructures), and easy to manufacture systems that employ novel and cutting edge evaporative and collection methods.
Using only basic physics and water chemistry, and the methods and devices disclosed herein, it will be common place to make fresh water from saline many times faster than ever thought possible or achieved before. The present disclosure is directed to methods and systems for increasing the rate and efficiency of liquid evaporation, which can be used for desalination. Through the use of kinetic energy input, which can be provided through an AC power grid or a non AC power grid energy source, and in certain embodiments in tandem with a gravity assist, the disclosed methods and systems overcome chemical and physical barriers and limits of the known evaporative and desalination methods and systems to simultaneously and substantially increase both the evaporation and the recovery/condensation capture rates. Several exemplary embodiments are presented, representing differences and variations in usage, scaled size, and logistics.